Question

A solid white substance A is heated strongly in the absence of air. It decomposes to form a new white substance B and a gas C. The gas has exactly the same properties as the product obtained when carbon is burned in an excess of oxygen. Based on these observations, can we determine whether solids \(A\) and \(B\) and gas \(C\) are elements or compounds? Explain your conclusions for each substance.

Short answer

In conclusion, based on the given information and the analysis of the decomposition reaction, we can determine that solid substance A is a compound and gas C is a compound (carbon dioxide). However, we cannot definitively classify solid substance B as an element or a compound without additional data.

Step-by-step solution

Identifying the Gas Produced from the Reaction

Since gas C has the same properties as the product obtained when carbon is burned in excess oxygen, we can infer that gas C is carbon dioxide (CO2). When carbon (C) is burned in excess oxygen (O2), it forms carbon dioxide: \[ C + O_2 \rightarrow CO_2 \] Now that we know gas C is carbon dioxide, let's analyze whether it's an element or a compound.

Classifying Gas C - Element or Compound

Gas C is carbon dioxide (CO₂), which consists of one carbon atom and two oxygen atoms. It is a chemical substance formed from two or more different elements (carbon and oxygen) bonded together. Therefore, gas C is a compound.

Analyzing the Decomposition Reaction of Substance A

The initial reaction described in the exercise involves the decomposition of substance A into substance B and gas C (carbon dioxide) when heated strongly in the absence of air: \[ A \xrightarrow{\Delta} B + CO_2 \] From this reaction, we can gather some information about substances A and B.

Classifying Substance A - Element or Compound

Since substance A decomposes to form a new substance B and carbon dioxide gas when heated, it must be composed of at least two different elements, as it produces multiple products. One of the elements in substance A must be carbon, as it is a component of the carbon dioxide produced. Therefore, substance A is not an element but a compound.

Classifying Substance B - Element or Compound

Substance B is formed when A decomposes, and since A was a compound containing carbon (and possibly other elements), substance B could be an element or a compound. Unfortunately, we cannot determine its classification as an element or compound based solely on the information provided in the exercise. We would need more data about substance B to make a conclusive decision. In conclusion: - Solid substance A is a compound. - Solid substance B cannot be definitively classified as an element or a compound based on the given information. - Gas C is a compound (carbon dioxide).

Key concepts

Chemical Compounds

Chemical compounds are substances that consist of two or more different types of elements bonded together in a fixed proportion. For example, water (H₂O) is a compound made of two hydrogen atoms bonded to one oxygen atom. The properties of compounds are distinct from the properties of their constituent elements. In our exercise, gas C, which is carbon dioxide (CO₂), is identified as a compound because it is made up of one carbon atom and two oxygen atoms chemically bonded together. Similarly, substance A is a compound because it decomposes into two different products, suggesting it was also composed of more than one element.

Understanding the nature of chemical compounds is crucial because it helps explain the variety of substances around us. Compounds have unique characteristics and behaviors which are different from the elements they are made from. This behavior is key in chemical reactions and is the foundation of chemistry as a science.

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into different substances. These processes are governed by the rearrangement of atoms as they break and form chemical bonds. In the context of our exercise, the heating of substance A in the absence of air leads to a decomposition reaction, which is a type of chemical reaction where a single compound breaks down into two or more simpler products. Here, substance A decomposes to give a new substance B and a gas C, which we've identified as carbon dioxide.

Decomposition reactions are critical to understand because they illustrate how compounds can be broken down into simpler substances. This concept is vital across various branches of chemistry including organic chemistry, where complex molecules are dissected into smaller components, and environmental chemistry, where decomposition plays a key role in the breakdown of organic matter.

Chemical Elements

Chemical elements are the simplest forms of matter that cannot be broken down into simpler substances by ordinary chemical means. Each element is characterized by the number of protons in its atomic nucleus, which is known as the atomic number. There are approximately 118 known elements, and they are the building blocks for all matter. While substance B from our exercise cannot be unequivocally classified as a compound or an element without additional information, we can utilize the concept of elements to ponder its identity. If substance B were composed of only one type of atom, it would be an element. If it contained more than one type, then it would be a compound.

Having a clear understanding of what defines an element is essential for mastering chemistry. Recognizing and working with elements is foundational in learning how substances interact and combine to form the vast array of materials we observe in the world.

Stoichiometry

Stoichiometry is the area of chemistry that pertains to the calculation of the quantities of reactants and products involved in chemical reactions. It is based on the conservation of mass and the concept of the mole, which allows chemists to count atoms, molecules, and ions. Stoichiometry involves using balanced chemical equations to determine the relationships between the amounts of substances. In the presented exercise, stoichiometry could help predict how much of substance B and gas C would form from a certain amount of substance A.

Mastering stoichiometry is fundamental since it equips students with the ability to predict product yields, identify limiting reagents, and adjust reaction conditions to achieve desired outcomes. It plays a pivotal role in everything from bench-top lab experiments to large-scale industrial processes where precise measurements and conversions are paramount.